MOSCOW (Reuters) - Russian patriotic bloggers expressed anger on Wednesday over the arrest of the former commander of Russia's 58th army, who was detained for fraud, and cast him as a talented general who had the courage to speak the truth to incompetent superiors.

Russia's state news agency TASS reported on Tuesday that Major General Ivan Popov had been arrested on suspicion of "large-scale fraud".

It was not possible to contact Popov directly, who Russian media said stood accused of stealing 100 million roubles ($1.1 million) of metal.

Following a June 2023 mutiny by Wagner mercenaries against Russia's defence establishment, Popov said he had been dismissed after telling the top brass about the dire situation at the front in Ukraine.

Popov, whose military call sign was "Spartacus" and who was popular with the troops, said at the time that Russian soldiers had been stabbed in the back because of the failings of their senior commanders.

"I know one thing: Ivan was at the head of the forces that repelled the enemy's counteroffensive," Alexander Sladkov, a war correspondent for Russian state television, said on Telegram.

"Stupid people are forgiven for lies and losses so others, I think, can be forgiven for the ruthless truth," he said. "General Ivan Popov is not a thief. He is a soldier. However... we also forgive thieves."

The support for Popov was widespread among pro-Russian military bloggers, who dismissed the allegations against him and cast Popov as a patriot who was being punished for speaking truth to power.

Popov was known for making a report in 2023 to Russia's top general, Chief of the General Staff Valery Gerasimov, which laid out the problems Russia faced on the front including lack of equipment, poor reconnaissance and infrequent rotation of troops.

According to military bloggers, Gerasimov - who preserved his position in a reshuffle earlier this month - was outraged at the bluntness of the report and accused Popov of spreading alarmist disinformation. The defence ministry did not comment.

Yuri Podolyaka, a popular pro-Russian military blogger, said he was in shock over the arrest.

"Commander Ivan Popov, in the summer of 2023, having built an excellent multi-lane line of defense in the band of his army (unlike many of his allies), in fact, saved our army from defeat and the country from shame."

Podolyaka said that Popov's defensive line was stronger than others and that his conflict with the general staff was well known in military circles.

"General Popov had the courage to speak to the very face of his superiors about those things which others, shyly lowering their eyes, preferred to keep silent," Podolyaka said.

After President Vladimir Putin was sworn in for a fifth time earlier this month, he appointed a new defence minister, Andrei Belousov, an economist who the Kremlin chief said would manage the ballooning defence spending on the war.

The changes at the defence ministry came after Deputy Defence Minister Timur Ivanov was detained on suspicion of bribe taking. Others have since been arrested as part of the probe.

Ivanov denies taking kickbacks worth about a billion roubles ($10.9 million).

($1 = 90.0925 roubles)

(Reporting by Guy Faulconbridge; Editing by Mark Trevelyan)